2000, gmc jimmy slt 4.3l, 4 door, 4x4
About 2 years ago when I got my jimmy the sending unit was shot, so my gas gauge would read as empty at all times, being that you can't replace just the sending unit, I replaced the pump with an Airtex fuel pump.

Now my current problem started, when I turn my vehicle to on the gas gauge jumps around until I acctually start the engine, then it stops, but not in the correct spot. After driving a bit I would settle where it should, but now most reacently the gas gauge doesn't read under half, I realized this when I did 220 miles on alittle over "half a tank" lol.

does this sound like the sending unit is going or maybe the gas gauge?
on a side note when I put the new harness pig tail on I used the wire crimp connectors, yes I am aware I should have soldered and shrink wrapped them, but I was a lot dumber when it came to vehicles then.
So maybe it could just be a wire came loose and is making intermittent connection? But if this was the case wouldn't it simply shoot between empty or full?

I'm leaning more towards sending unit though.

 

Very common issue on these. Most folks swear at Airtex pumps-I have never had a problem with them in these or other vehicles. It does indeed sound like the sending unit is faulty. There is also a ground at the rear of the unit that can contribute to incorrect readings-the gauge itself can only supply the info available and rarely goes bad IMO. Search this site and you will have an answer. My sending unit is bad in my 97 and as the pump was replaced prior to my owning it and the pressure is great,I just fill it when ever I cover over 250-270mi and reset the meter and off I go again....

 

The fuel level sending unit can be serviced separately. Loose or poor connections at the new module connector, and or body ground, will cause the dash gauge to read higher than actual fuel level. A "bouncing" dash gauge is caused by a bad buffer, (electrical "shock absorber") in the fuel level sender, common problem with aftermarket level senders.